The present invention relates to the improvement of a lubricating system for a toroidal continuously variable automatic transmission for automotive vehicles.
One such toroidal CVT has been disclosed in Japanese Patent Provisional Publication No. 5-39847 (hereinafter is referred to as xe2x80x9cJP5-39847xe2x80x9d). The toroidal CVT is equipped with a lubricating system generally composed of a trunnion lubrication system mainly used for lubrication of spherical joints and needle bearings of upper and lower links and for lubrication and cooling of power rollers and input and output disks, and a rolling contact surface lubrication system used for lubrication of rolling contact surfaces between the power roller and input and output disks. Usually, some of pressure oil discharged from a hydraulic pump passes through an oil cooler and then the properly-cooled traction oil is supplied to both a trunnion lubricating oil passage and a rolling contact surface lubricating oil passage for lubricating and cooling the power roller and trunnion and for lubricating and cooling the rolling contact surfaces of the power roller and input and output disks. After lubrication, almost all of the oil drains back into an oil reservoir (or an oil tank or an oil pan). However, in the conventional lubricating system of the toroidal CVT as disclosed in JP5-39847, during cold engine start, or when the traction oil is cooled excessively by the oil cooler and the excessively cooled oil is supplied to the rolling contact surfaces, decreasing oil temperature causes a film of oil adhered to the rolling contact surface to thicken and have a thigh coefficient of viscosity. The thicker oil film of the rolling contact surface lowers a traction coefficient. As is generally known, the oil (exactly, traction oil) adhered to the rolling contact surface functions as a power-transmission element, and thus it is necessary to maintain the thickness of the film of traction oil adhered to the rolling contact surface at a proper oil thickness. The oil thickness of traction oil adhered to the rolling contact surface is dependent upon the oil temperature.
It is desirable that the oil temperature control (or oil temperature management) of oil used for lubrication and cooling required for the moving parts located inside of the power roller is different from the oil temperature control (or oil temperature management) of oil serving as the power-transmission element and adhered to used for the rolling contact surface of the power roller. In particular, when the engine is temporarily stopped under a condition that the toroidal CVT unit is not sufficiently warmed up after the cold engine start-up, a very thick traction oil film is formed on the rolling contact surface. Under this condition, when a selector lever is shifted from a neutral range to a D range or to a R range, in order to prevent slippage between the power roller and input and output disks, it is necessary to increase a spring stiffness of a dished-plate spring pre-loading or biasing the input and output disks in the axial direction, and/or it is necessary to increase the inclination angle of the cam contour surface of a loading cam that axially presses the associated input disk so as to increase a loading force created by the loading cam and varying depending on the magnitude of input torque. Properly increasing the loading force is effective to prevent undesired slippage between the power roller and input and output disks. Excessively increasing the loading force, on the other hand, deteriorates a power transmission efficiency, thus deteriorating fuel economy. To avoid this, if a heater is provided within the oil pan, it takes a long time required to warm a large amount of oil stored in the oil pan. With the heater built in the oil pan, a remarkable effect cannot be brought when the engine is started from a state that the toroidal CVT unit is cold. To produce the remarkable effect of properly warmed-up traction oil, a large capacity of heater must be provided in the oil pan. This is improper from the viewpoint of lightening, increased layout flexibility, reduced production costs, and a reduced storage-battery capacity.
Accordingly, it is an object of the invention to provide a lubricating system for a toroidal continuously variable transmission, which avoids the aforementioned disadvantages.
It is another object of the invention to provide a lubricating system for a toroidal continuously variable transmission equipped with at least a first lubricating circuit for lubrication of rolling contact surfaces of a power roller and input and output disks and a second lubricating circuit for lubrication of moving parts of the power roller and trunnions, which is capable of creating a traction oil film having a proper thickness on the rolling contact surfaces even when an oil temperature is low just after starting wit a cold engine.
In order to accomplish the aforementioned and other objects of the present invention, a lubricating system for a toroidal continuously variable transmission equipped with a trunnion rotatably supporting a power roller gripped between input and output disks so that a gyration angle of the power roller is variable, comprises a first lubricating circuit provided for lubrication of a rolling contact surface on which the input and output disks are in friction-contact with the power roller, a second lubricating circuit provided for lubrication of the trunnion and the power roller, and an oil-temperature control device provided in the first lubricating circuit for heating oil of the toroidal continuously variable transmission, so that the oil temperature-controlled by the oil-temperature control device is supplied through the first lubricating circuit into the rolling contact surface.
According to another aspect of the invention, a lubricating system for a toroidal continuously variable transmission equipped with a trunnion rotatably supporting a power roller gripped between input and output disks so that a gyration angle of the power roller is variable, comprises a rolling contact surface lubrication circuit provided for lubrication of a rolling contact surface on which the input and output disks are in friction-contact with the power roller via traction oil, a trunnion lubrication circuit provided for lubrication and cooling of the trunnion and the power roller, and an oil-temperature control means provided in the rolling contact surface lubrication circuit for temperature-controlling the traction oil, so that the traction oil temperature-controlled by the oil-temperature control means is supplied through the rolling contact surface lubrication circuit into the rolling contact surface.
According to a further aspect of the invention, a method for independently temperature-controlling traction oil in a dual circuit lubricating system for a toroidal continuously variable transmission equipped with a trunnion rotatably supporting a power roller gripped between input and output disks so that a gyration angle of the power roller is variable, the dual circuit lubricating system having a first lubricating circuit for lubrication of a rolling contact surface on which the input and output disks are in friction-contact with the power roller via the traction oil, a second lubricating circuit for lubrication and cooling of the trunnion and the power roller, an oil heater heating the traction oil and an oil cooler cooling the traction oil, the method comprises detecting a condition of an operating temperature of the toroidal continuously variable transmission, determining, responsively to the condition of the operating temperature detected, as to whether the toroidal continuously variable transmission is in a cold-transmission state or in a hot-transmission state, supplying the traction oil cooled by the cooler via the second lubricating circuit for lubrication and cooling of the trunnion and the power roller, supplying the traction oil temperature-risen by the heater via the first lubricating circuit for lubrication of the rolling contact surface when the toroidal continuously variable transmission is in the cold-transmission state, and supplying the traction oil temperature-fallen by the cooler via the first lubricating circuit for lubrication of the rolling contact surface when the toroidal continuously variable transmission is in the hot-transmission state.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.